King County Metro Transit's new three-story garage at a busy Eastside park-and-ride near State Route 520 is open for commuters, and officials marked the milestone at a ceremony Tuesday where they also highlighted the need for stable, ongoing transportation funding.

"The riders streaming into this hub are visible evidence of the growing transit demand here on the Eastside," said King County Executive Dow Constantine. "People and businesses need bus service, and we must stay focused on getting stable funding that averts the drastic service cuts on the horizon."

The cities of Bellevue and Kirkland collaborated to help make the project a reality. "Public transportation is contributing to a better quality of life on the Eastside, and the local economy is thriving because transit has kept the region moving," Bellevue Mayor Conrad Lee said.

The new garage on the Bellevue-Kirkland border opened Sept. 5 and has 530 parking spaces, plus 260 spaces in the surface parking lot. The lot used to have about 600 spaces, and will top out at 850 spaces next year once construction is complete on the mixed-use housing project next door. Together, the garage and housing comprise a transit-oriented development (TOD), successfully concentrating housing and a transit hub to reduce the need to drive or own a vehicle.

King County provided $8.8 million in funding toward building the transit center and garage, largely from grants by the Federal Transit Administration and the state Department of Transportation. Developer Polygon Northwest received funding and the housing parcel in compensation for building the garage and transit center.

For Seattle and Eastside job centers, the location is central along State Route 520, which has seen 25 percent growth in ridership due to increased service and demand since 2010.

The mixed-income, mixed-use housing development will include 243 apartments and is slated to open for initial occupancy in fall 2014. Polygon Northwest is building 185 residences, approximately 7,000 square feet of retail and 287 additional parking spaces for residents. Local nonprofit affordable housing developer Imagine Housing and its affiliate, Red Vines 1, will build and operate 58 affordable residences.